Multi-speed transmissions are typically provided in material handling implements and agricultural equipment to facilitate efficient performance of various work operations. While a number of different types of multi-speed transmissions are known, one arrangement which has found particular suitability in this type of equipment includes a plurality of hydraulically-operated clutches. Selective fluid pressurization of any one of the clutches effects selection of an associated one of a plurality of speed ratios. In such arrangements, the gears of the associated gear set are typically in constant mesh, with selective pressurization of the associated clutch functioning to couple one of the gears in power-transmitting relation with the clutch, thus transmitting power through the gear set.
In a typical construction including a hydraulically-operated clutch and an associated gear set, the clutch is mounted on a transmission shaft for rotation therewith, with the gear to be selectively coupled with the clutch positioned on the shaft in generally adjacent relation to the clutch. A plurality of annular clutch friction plates are provided generally within the clutch assembly, with the friction plates typically coupled to the associated gear by splines or the like for rotation therewith. Clutch separator plates are further provided between adjacent ones of the friction plates, with the annular separator plates including means whereby they are coupled for rotation with the clutch housing and transmission shaft. A hydraulically pressurized clutch piston is provided for urging the separator plates and friction plates into frictional engagement with each other, whereby the gear is coupled in power-transmitting relation with the clutch and shaft.
A hydraulically-operated clutch of this nature is frequently configured as a "wet" clutch, i.e., one in which lubricant is generally continuously supplied to the clutch assembly. In a typical construction, lubricant passages are provided in the gear and the transmission shaft such that pressurized lubricant is introduced into the assembly generally at the splined interface of the gear and the clutch friction plates. The lubricant typically flows axially out of the assembly between the clutch and the gear, and also flows radially out of the assembly between the clutch friction plates and separator plates. Lubricant flow radially out of the clutch can occur by flow through grooves defined by the friction surfaces of the friction plates, in that such grooves provide flow paths between the inner peripheries of the plates and their outer peripheries. Grooves of this nature are ordinarily provided in the friction material so that upon clutch engagement, lubricant is quickly "sheared" or "wiped" from the friction surfaces of the clutch plates for quickly establishing positive engagement.
While the above-described hydraulic clutch arrangement has been in widespread use, problems of premature wear have been experienced in some applications. In particular, premature wear of the spline teeth of the clutch friction plates at their splined connection to the associated gear has been experienced. This unusual wear is believed to have resulted from the friction plates being subjected to oscillation during operation of the transmission, with the oscillation creating sufficient friction to form minute welds between the spline teeth of the friction plate and the splines of the gear. Fracture of these minute welds results in particles of material being present at the spline interface, with such material acting as an abrasive such that grooves are worn into the gear spline teeth, and the spline teeth of the friction plate are worn to a pointed condition. In extreme cases, this "fretting" wear has resulted in breaking of the friction plate spline teeth.
In the past, various attempts have been made to correct the premature wear of the splined interface between the clutch friction plates and the associated gear. Attempts to solve the problem have included subjecting the spline teeth of the friction plates to additional hardening treatment, reconfiguring the spline teeth to be of a relatively greater thickness, reconfiguring the splined connection to one of a coarser pitch, and improving the support of the gear mounted on the transmission shaft in an effort to minimize eccentric motion thereof that contributes to the above wear problem. However, these various solutions were found to only provide a small increase in the useful service life of the construction.
Upon further investigation and testing of this wear phenomenon, it was determined that an improved arrangement for effecting lubrication of the clutch assembly significantly abates the above-described wear problem, thus significantly contributing to the useful service life of the transmission.